Such a disc is known from U6496541 where a channel code for recording an optical disc is disclosed. This 17PP channel code is parity preserving. To create watermarks on the optical disc such a code is extended with extra code words so that when encoding a choice exists between code words that yield higher or lower reflectivity. This is however not always possible if most code words are already used by the code and not many additional unused code words are available, so that the result is of low quality because not always the optimal reflectivity can be obtained. In addition adding extra code words to the code means that the decoder has to be modified in order to correctly decode these additional code words, resulting in a loss of backwards compatibility with the installed base.
The visual pattern is a form of watermark allowing the inspection of the disc to determine whether it is a genuine disc or not.
Watermarking and other copy protection measures are taken to stop home copying and professional pirates.
The known record carriers with such a watermark also have the problem that these discs can be duplicated by professional Laser Beam Recorders (LBR's). An LBR is a professional mastering machine for optical discs. The duplication of a record carrier with the known watermarks using such a Laser Beam Recorder is difficult to distinguish from the original record carrier.